This invention relates to rotary worm compression-expansion machines and more particularly, it concerns a novel thread configuration for the rotors of such machines.
The disclosures of U.S. Pat. No. 3,180,565, issued Apr. 27, 1965, U.S. Pat. No. 3,632,239 issued Jan. 4, 1972 and U.S. Pat. No. 3,905,731 issued Sept. 16, 1975, all to the inventor, Bernard Zimmern, exemplify the current state-of-the-art relative to rotary worm compression-expansion machines. In such machines, a single threaded rotor is contained in a housing so that each groove lying between a pair of threads defines with the housing an elongated chamber. As the threaded rotor rotates relative to one or more pinion wheels carried by the housing for rotation on axes tangential to the rotor, each groove is swept by a pinion wheel tooth. Compression (or expansion) of fluid in each groove occurs due to the positioning of outlet porting in the housing relative to pinion wheel location.
The machine rotors may be of either generally cylindrical or conical configuration, the latter being preferable for increased volumetric capacity due to a facility for providing concentric spiral threads on opposite sides of a single rotor, the threads on each side being cooperable with two pinion wheels. The structural organization of such a conical screw machine which has demonstrated significant commercial potential as a high capacity air compressor is fully disclosed in the last issued of the afore-mentioned U.S. Pat. No. 3,905,731.
In the operation of a conical screw machine of this type, pinion wheel teeth enter each thread groove in the rotor screw at the outside diameter of the rotor and move inwardly, following the spiral thread groove to a minimal radius on completion of each work cycle. The tangential speed of the rotor at its outside diameter is, of course, greater and this factor combined with the closure of each groove by a pinion wheel tooth at the outer diameter of the rotor can impose shock loading on the pinion wheel teeth. In addition, the relative speed of movement between rotor thread grooves and pinion wheel teeth at the outer peripheral edge of the rotor contributes an increase of friction resulting in pinion wheel wear. While machine designs in the prior art have shown substantial promise from the standpoint of providing a relatively simple, well-balanced and quiet operating air compressors, there is need for improvement from the standpoint of providing longer useful life of the pinion wheels used in such machines.